Biomedical subjects

H Takagi

Publications and source records attributed to H Takagi.

At least 127 records · Page 7Linked to original sources

PubMed2000

Absence of residual quasiparticle conductivity in the underdoped cuprate YBa2Cu4O8.

We report measurements of the in-plane thermal conductivity kappa of the stoichiometric underdoped cuprate YBa2Cu4O8 (Y124) below 1 K. kappa(T) is shown to follow a simple phononic T3 dependence at the lowest temperature T for both current directions, with a negligible linear quasiparticle contribution. This observation is in marked contrast with behavior reported in optimally doped cuprates, and implies that extended zero-energy (or low-energy) quasiparticles are absent in Y124.

Journal Article↗

PubMed2000

Time-sharing contributions of A- and D-type K+ channels to the integration of high-frequency sequential excitatory post synaptic potentials at a model dendrite in rats.

A- and D-type K+ channels (KA and KD channels) have unique physiological properties that play important roles in the integration of excitatory post synaptic potentials (EPSPs) in neuronal dendrites. These functions were analyzed using a computer program, NEURON, to simulate high-frequency sequential synaptic inputs, that can induce long-term potentiation (LTP). We paid close attention to the stability of the reduction of sequential EPSPs. When either KA or KD channels were included in models, the EPSP reduction ratios were less stable than containing both KA and KD channels. When both KA and KD channels were present in the model, the variance of EPSP reduction ratios was significantly smaller in comparison with that in the presence of either KA or KD channels alone. We thus concluded that the co-existence of KA and KD channels is necessary to produce stable EPSPs during the high-frequency synaptic stimulation necessary for induction of LTP.

Animals↗

PubMed2000

LiV2O4 spinel as a heavy-mass fermi liquid: anomalous transport and role of geometrical frustration

Transport and specific heat measurements on hydrothermally grown single crystals reveal the formation of a heavy-mass Fermi liquid in the LiV2O4 spinel, below a coherence temperature of T* = 20-30 K. A few observations which illustrate the uniqueness of this spinel are discussed in connection with the origin of the heavy mass, such as the anomalous absence of resistivity saturation above T* and the close proximity to a spin glass phase where the influence of the magnetic frustration is evident.

Journal Article↗

PubMed2000

Holes in a Quantum Spin Liquid.

Magnetic neutron scattering provides evidence for nucleation of antiferromagnetic droplets around impurities in a doped nickel oxide-based quantum magnet. The undoped parent compound contains a spin liquid with a cooperative singlet ground state and a gap in the magnetic excitation spectrum. Calcium doping creates excitations below the gap with an incommensurate structure factor. We show that weakly interacting antiferromagnetic droplets with a central phase shift of pi and a size controlled by the correlation length of the quantum liquid can account for the data. The experiment provides a quantitative impression of the magnetic polarization cloud associated with holes in a doped transition metal oxide.

Journal Article↗

PubMed2000

Neutron diffraction evidence of microscopic charge inhomogeneities in the CuO2 plane of superconducting La2-xSrxCuO4 (0<or=x<or=0. 30).

High-resolution atomic pair distribution functions have been obtained using neutron powder diffraction data from La2-xSrxCuO4 over the range of doping 0<or=x<or=0.30 at 10 K. Despite the average structure getting less orthorhombic, we see a broadening of the in-plane Cu-O bond distribution as a function of doping up to optimal doping. Thereafter the peak abruptly sharpens. The peak broadening can be well explained by a local microscopic coexistence of doped and undoped material. This suggests a crossover from a charge inhomogeneous state at and below optimal doping to a homogeneous charge state above optimal doping.

Journal Article↗

PubMed2000

Lack of susceptibility of transgenic mice carrying the human c-Ha-ras proto-oncogene (rasH2 mice) to phenolphthalein in a 6-month carcinogenicity study.

Phenolphthalein has carcinogenic activity, causing malignant lymphomas in B6C3F1 mice at a dietary dose of 3000 ppm in a 2-year carcinogenicity study and in heterozygous p53-deficient female mice at the same dose in a 6-month study. To examine whether phenolphthalein carcinogenic potential can be detected in male and female transgenic (Tg) mice carrying the human c-Ha-ras gene (rasH2 mice) and their wild-type littermates (non-Tg mice), a diet containing 3000, 6000 or 12000 ppm was given for 6 months. Unequivocal induction of neoplastic lesions was not apparent, suggesting that rasH2 mice are resistant to the induction of malignant lymphomas by the treatment of phenolphthalein.

Adenoma, Liver Cell↗

PubMed2000

Dynamical aspects of the photoinduced phase transition in spin-crossover complexes

We report a dynamical study on the photoinduced cooperative changes of the spin configurations in single crystals of the organometal spin-crossover complex. In the photoswitching process between low- and high-spin states, nonlinear characteristics such as thresholdlike behavior, incubation period, and phase separation have been observed. These results demonstrate that the cooperative intersystem crossing mediated by spin-lattice interaction plays a key role in the driving process of a new class of nonequilibrium phenomena so called photoinduced phase transition.

Journal Article↗

PubMed2000

Proline accumulation by mutation or disruption of the proline oxidase gene improves resistance to freezing and desiccation stresses in Saccharomyces cerevisiae.

We examined the role of intracellular proline under freezing and desiccation stress conditions in Saccharomyces cerevisiae. When cultured in liquid minimal medium, the proline-nonutilizing mutant containing the put1 mutation (proline oxidase-deficient) produced more intracellular proline, and increased the cell survival rate as compared to the wild-type strain after freezing and desiccation. We also constructed two PUT1 gene disruptants. PUT1-disrupted mutants in minimal medium supplemented with external proline at 0.1% accumulated higher proline levels than those of the control strains (17-22-fold). These disruptants also had a 2-5-fold increase in cell viability compared to the control strains after freezing and desiccation stresses. These results indicate that proline has a stress-protective function in yeast.

Adaptation, Physiological↗

PubMed2000

Idiopathic portal hypertension associated with systemic lupus erythematosus.

A case of idiopathic portal hypertension (IPH) associated with systemic lupus erythematosus (SLE) is reported in a 38-year-old man who had been diagnosed with SLE and treated for 18 years. Esophageal varices. found in 1994 on endoscopic examination, had been followed up for 2 years. On July 16, 1996, he was admitted to Nagoya University Hospital because there was a high risk of bleeding from the esophageal varices due to severe thrombocytopenia. As partial splenic embolization had temporarily controlled the thrombocytopenia, splenectomy and devascularization of the stomach vessels were performed after endoscopic ligation of the esophageal varices. Histological specimens of wedge biopsied liver showed chronic inactive hepatitis without cirrhosis. The presence of anticardiolipin antibody, indicated by positivity for lupus anticoagulant, was suggestive of the presence of a common immunological mechanism in the etiology of SLE and IPH.

Adult↗

PubMed2000

Hepatocellular carcinoma complicated by hemothorax.

Although hemoperitoneum is a well-known cause of death induced by rupture of hepatocellular carcinoma (HCC). hemothorax caused by rupture of HCC has not been adequately described. We report here a 64-year-old woman who died of bleeding from pleural wall metastasis of HCC. She presented with liver failure and sudden-onset hypotension, and on the same day, she died of hypovolemic shock associated with liver failure. Autopsy revealed HCC metastatic to the lungs and right pleura and 21 of bloody pleural effusion in the right side. The cut surface of the metastatic nodule in the right pleura was filled with coagulated blood and necrotic tissue. We concluded that the pleural metastasis had ruptured and caused the right hemothorax. We discuss reported cases of HCC complicated by hemothorax.

Carcinoma, Hepatocellular↗

PubMed2000